SURFACE MIGRATION OF HOT ADATOMS IN THE COURSE OF DISSOCIATIVE CHEMISORPTION OF OXYGEN ON AL(111)

Scanning tunneling microscopy observations on an Al(111) surface reveal that O adatoms at 300 K are practically immobile. Low-coverage overlayers formed by dissociative chemisorption of O2 consist essentially only of single isolated atoms rather than of pairs of adjacent atoms. Hence upon dissociation at least part of the chemisorption energy must be transformed into translational energy parallel to the surface which causes the two O atoms formed to separate from each other by at least 80 angstrom before the excess energy is dissipated. The lifetime of these "hot" adatoms is estimated to be on the order of greater-than-or-equal-to 1 ps.